1. Field of the Invention
The present invention relates to a chucking device for chucking a work implemented as a hollow, cylindrical member.
2. Description of the Background Art
A chucking device including an elastic member that inflates when filled with compressed air or compressed liquid is conventional. Assume that the chucking device is applied to the production of a photoconductive element for electrophotography. Then, the chucking device chucks the hollow, cylindrical base of the photoconductive element with the elastic member being inflated and pressing itself against the inner periphery of the base. The chucking device then dips the base in a coating liquid to thereby uniformly coat the former with the latter. To insure high-quality images free from irregular density and background contamination, it is necessary to prevent compressed air inside the elastic member from leaking to a space in the lower portion or the upper portion of the base. It is also necessary to cause the elastic member to closely contact the inner periphery of the base for thereby surely sealing the inside of the base.
Japanese Patent Laid-Open Publication No. 4-4034, for example, teaches a chucking device including a rubber sack. The rubber sack is inserted into a hollow, cylindrical base and then inflated by compressed air, contacting substantially the entire inner periphery of the base except for the bottom opening of the base. Japanese Patent Publication No. 7-38964 discloses a chucking device including an upper and a lower pressing member having tapered surfaces facing each other. The upper and lower pressing members crush an annular elastic member and thereby cause the elastic member to press itself against the inner periphery of a hollow, cylindrical base.
The chucking device taught in the above Laid-Open Publication No. 4-4034 has some problems left unsolved, as will be described hereinafter. The rubber sack is expected to press itself against substantially the entire inner periphery of a hollow, cylindrical base. Therefore, a long period of time is necessary to check whether or not the rubber sack is defective, making maintenance inefficient. During usual, dip coating process (e.g., continuous coating of a first pallet to a tenth pallet), the rubber sack whose thermal conductivity is low covers substantial the area of the inner periphery of the base except for the bottom opening. Therefore, when the base is lifted out of the coating liquid, the coating liquid evaporates and takes heat from the base and film formed thereon. This heat is accumulated in the rubber sack with the result that the surface temperature of the base sequentially decreases from the first pallet to the tenth pallet, causing the temperature of the coating liquid to drop. Consequently, the viscosity of the coating liquid and therefore the thickness of the film increases. That is, the cooling of the chucking device itself brings about this problem.
The chucking device taught in Publication No. 7-38964 is free from the cooling problem because it contacts the inner periphery of the base over a minimum of area. However, the chucking device crushes the annular elastic member and therefore accelerates the deterioration of the elastic member, i.e., limits the life of the elastic member. Moreover, the upper and lower pressing members are pressed against the elastic member by springs, causing the elastic member to deform. This, however, cannot surely cause the elastic member to closely contact the inner periphery of the base.
It is an object of the present invention to provide a chucking device minimizing an area over which an annular elastic member contacts the inner periphery of a hollow, cylindrical base and causing the elastic member to surely contact the above inner periphery and insure sealing, thereby insuring uniform film thickness.
A chucking device of the present invention includes an annular elastic member sandwiched between an upper and a lower member. A rod is slidable up and down in a bore formed in the upper and lower members and is partly positioned in the elastic member. The rod presses the elastic member radially outward when raised or lowered, thereby causing the chucking device to chuck a hollow, cylindrical base. The elastic member contacts the inner periphery of the base over a minimum of area and surely, closely contacts it for thereby implementing desirable sealing. The chucking device can therefore form a uniform film on the outer periphery of the base.